This invention relates generally to saving data in a storage space, in particular to saving data in a multi-tiered virtual storage space while the storage space is active.
Virtualization of storage allows a controlling operating system to carve out a large portion of the overall space to be allocated to a server. For example, on a system, such as an IBM system i5/OS®, large network server storage spaces can be created that are 1 terabyte in size and can be linked to a hosted operating system, like Linux, AIX, or Windows. The hosted operating system views this storage space as a single disk drive that can be partitioned and formatted like any other disk. This storage space can be saved and restored using an integrated operating system, since it is actually just a file accessible in the integrated file system.
However, to save this storage space while active requires the hosted operating system to be made aware that some higher level operating system needs to save the entire disk drive and to prepare for a backup. This means all data in cache needs to be written to disk. Once data on the disk is made consistent, a save-while-active process needs to take a snapshot of the object so no future write requests will affect the save and cause the data to be inconsistent. The save-while-active process uses a copy-on-write approach so only the data at the point of the “snapshot” will be saved.
The problem with this solution is that there is no process defined to prepare a hosted operating system for backup to allow the storage space to be saved safely and consistently. What makes this scenario even more difficult is if the hosted operating system also becomes a host to other operating systems using Microsoft virtual servers or using VMWare virtual servers. Since there is no way to safely save this storage space with consistent data, the only safe process to save a storage space, up to now, has been to have the hosted operating systems shut down so all data on the disk is consistent and will not change throughout the save.